The purpose of the auditory system in mammals is to convert sound (pressure) waves into electrical signals that the brain can interpret. The human ear 1 is divided into the outer ear 10, the middle ear 20, and the inner ear 30 as shown in FIG. 1 and explained, for example, in Reece et al., Campbell Biology at pages 1090-94 (9th ed., Pearson Education Inc., 2011). The outer ear 10 includes the pinna 12, a curved external cartilage which “catches” sound waves and directs them into the auditory canal 14. At the end of the auditory canal 14, separating the outer ear 10 and the middle ear 20, is the eardrum 16. The eardrum 16 is also known as the tympanic membrane, is taut, and is pushed inward and outward via sound pressure waves.
The three bones of the middle ear 20 are collectively called the ossicles or the auditory ossicles. Starting proximate the eardrum 16, the bones are the malleus 22 (also known as the hammer), the incus 24 (also known as the anvil), and the stapes 26 (also known as the stirrup). The ossicles are contained within the middle ear 20 and transmit sounds from the air to the fluid-filled labyrinth called the cochlea 32, which is located in the inner ear 30 along with the semicircular canals 34. The ossicles are arranged so that movement of the eardrum 16 causes movement of the malleus 22, which causes movement of the incus 24, which causes movement of the stapes 26. The ossicles are coupled to the eardrum 16 and consequently vibrate when the eardrum 16 oscillates. All the vibrational energy of the eardrum 16 is concentrated on the much smaller surface area of the ossicles. This increases the pressure about fifteen to thirty times, thereby amplifying the sound.
Once a sound propagates through the middle ear 20, it comes to the faceplate of the stapes 26 resting against the cochlea 32, which is the starting point of the inner ear 30. Thousands of hair-like nerve cells line the length of the cochlea 32. Each hair cell has a particular resonant frequency. When the stapes 26 vibrates in the middle ear 20, it strikes the faceplate of the cochlea 32. The round window 36 is one of the two openings into the inner ear 30. The round window 36 is closed from the middle ear 20 by the round window membrane, which vibrates and moves fluid in the cochlea 32, which in turn ensures that hair cells of the basilar membrane will be stimulated. Thus, the strike of the stapes 26 sends a compression wave through the cochlea 32 and, as the wave travels, if its frequency matches with the natural frequency of any hair cells, those hair cells will resonate and vibrate with larger amplitude. This increased movement initiates nerve cells to emit electrical impulses to the brain for processing.
More specifically, the vestibulocochlear nerve has two branches: the vestibular nerve 52 and the cochlear nerve 54. The vestibular nerve 52 transmits spatial orientation information from the three semicircular canals 34 to the brain. The cochlear nerve 54 carries signals from the cochlea 32 of the inner ear 30 directly to the brain.
The middle ear 20 opens into the Eustachian tube 40, which connects to the pharynx via the opening 42 and equalizes pressure between the middle ear 20 and the atmosphere. The balance portion of the inner ear 30 includes the three semicircular canals 34. Arterial supply of blood to the ear 1 is provided, in part, through the internal carotid artery 50. The styloid bone 56 is a slender pointed piece of bone just below the ear 1. The styloid bone 56 projects down and forward from the inferior surface of the temporal bone, and serves as an anchor point for several muscles associated with the tongue and larynx.
The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range). Although hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear 1, human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear 30, rather than in the nerves or tracts of the central auditory system. There are two types of deafness: conductive and sensorineural. Conductive deafness occurs when sound waves cannot enter the inner ear 30. Usually caused by physical impedance, conductive deafness can result from infection, perforation of the eardrum 16, loud noises, etc. Sensorineural deafness most commonly involves damaged hair cells, auditory nerves, or auditory processing in the brain. Sensorineural deafness can be caused by genetics, viral infections, inflammation, multiple sclerosis, and stroke.
A number of solutions have been proposed to address the problem of deafness. For example, U.S. Pat. No. 8,396,239 issued to Fay et al. discloses an optical electro-mechanical hearing device with combined power and signal architectures. An audio signal transmission device includes a first light source and a second light source configured to emit a first wavelength of light and a second wavelength of light, respectively. The first detector and the second detector are configured to receive the first wavelength of light and the second wavelength of light, respectively. A transducer electrically coupled to the detectors is configured to vibrate at least one of an eardrum or ossicle in response to the first wavelength of light and the second wavelength of light. The first detector and second detector can be coupled to the transducer with opposite polarity, such that the transducer is configured to move with a first movement in response to the first wavelength and move with a second movement in response to the second wavelength, in which the second movement opposes the first movement.
Others have addressed the problem of deafness by converting sound signals into other media. In U.S. Pat. No. 3,766,311, for example, Boll teaches a sensory substitution system. The system converts electrically coded information into selective, intelligible, localized cooling of a receptive heat-producing medium, e.g., a human body. In combination with a microphone, amplifier, and filters for producing the electrically coded information, the system enables a deaf person to perceive auditory information in the form of distinguishable localized cooling of the skin. Advantageously, the selective, localized cooling of the skin is achieved by covering a portion of the body with an apertured insulating medium and selectively gating body-produced heat through the medium. In preferred embodiments, the selective gating is achieved by a vibrating disc driven by a vibrating reed which, in turn, is driven by a piezoelectric element.
Similarly, in U.S. Patent Application Publication No. 2010/0013612, Zachman discloses an electro-mechanical system designed to help the hearing impaired. The system has a plurality of servo actuators each associated with a particular segment of a predetermined frequency domain. The servo actuators drive tactile stimulators which engage the skin of the hearing-impaired person in patterns that are unique to individual inputs thereby enabling the hearing-impaired person to “hear” signals within the defined frequency domain.
Others seek to assist the deaf by proposing methods and devices for image display of sound waves. For example, in U.S. Pat. No. 3,831,434, Greguss discloses an apparatus that uses a piezo-optic cell having a thin layer of aligned liquid crystals which is illuminated by polarized light and viewed through a polarized analyzer to give a real-time visual image in color of the acoustic wave pattern incident on the cell. The acoustic wave pattern is typically an acoustic image of an insonified object such that the resulting device is useful in non-destructive testing for industry and medicine. The acoustic wave pattern can also be the human voice (helpful in teaching speech to the deaf) and music (for pleasurable and informative visualization of the musical sound). By use of a reference acoustic wave this device may be utilized to obtain a holographic image.
Despite the existence of the devices summarized above, science educators have yet to address many of the problems that arise when attempting to teach deaf or hearing-impaired students. One of the important responsibilities for such educators is ensuring that students possess the proper tools and accommodations to examine phenomena in a laboratory setting. It is the job of the educator to innovate methods and devices that enable students with disabilities to participate in all aspects of investigations.
None of the existing devices summarized above can be used in an educational setting to demonstrate hearing sensitivity to a deaf or hearing-impaired person. To overcome the shortcomings of the existing devices, a new electro-optical eardrum is provided as part of an experimental educational system. An object of the present invention is to provide a real-time display of the sound suitable for educational applications and the like. A related object is to reproduce adequately sounds with frequencies between 20 Hz and 20 kHz (the audio range). Another object is to avoid physically contacting the student, and particularly the skin of a person, especially via a device that must be worn or carried on the person. It is still another object of the present invention to use relatively simple and inexpensive components, which fall within the limited budgets of educational institutions, while avoiding components that are complex, expensive, or both.
An introductory physics laboratory experiment at a typical university guides students through several computer simulations investigating the properties of waves and wave interference. After the simulations, students are prompted to determine the minimum and maximum frequencies they can hear using a basic function generator and headphones. Educators have inadequately addressed, to date, the problem of how they would include a deaf student in the experiment while the other students are listening to headphones to determine their personal hearing sensitivities. Therefore, a need exists to allow a student, particularly but not limited to a deaf student, to determine the hearing sensitivity of an electro-optical eardrum when unable to do so personally and without assistance.